They allege that the service, which is used to spread uncensored news and political opinions, is rife with extremist propaganda and child pornography.

Telegram CEO Pavel Durov said "the real reasons" for the charges were far different, suggesting this newest controversy merely represents the latest back-and-forth between the government and the app, which millions of Iranians use.

A report Tuesday by the ISNA news agency quoted Tehran prosecutor Abbas Jafari Dolatabadi as saying the charges against Durov stem from Telegram's popularity with the Islamic State group, as well as the ease by which child pornographers, human traffickers and drug smugglers could use the app.

Dolatabadi also reportedly said that "Western law" didn't apply to this case. He said the unspecified charges now were in the hands of the international affairs division of Tehran's prosecutor.

It remains unclear how Iran will prosecute Durov as he lives outside of the country.

Durov wrote on Twitter that he was surprised by the comments.

"We are actively blocking terrorist and pornographic content in Iran," he wrote. "I think the real reasons are different."

Telegram remains wildly popular in Iran, where government authorities ban social media websites like Facebook and Twitter and censor other websites. Iran's young and tech-savvy citizens use virtual private networks or other workarounds to bypass those controls, while government officials have wide access.

Telegram, however, is open and uncensored, with massive group lists sending everything from poems to political screeds. During the presidential election earlier this year, hard-liners and reformists alike used the app to share information.

Telegram touts itself as being highly encrypted and allows users to set their messages to "self-destruct" after a certain period, making it a favorite among activists and others concerned about their privacy. That has made it a target of Iranian authorities in the past.

In July, Iran's new communications and information technology minister alleged that Telegram had transferred some of its servers into the country.

Durov disputed that, saying Telegram planned only to use content delivery networks, or CDNs, in Iran. He said those CDNs, which make data available faster, are not able to decipher encrypted messages sent by Telegram.